Testing and Commissioning of Electrical Equipment’s | Set 2
1. What is the actuating quantity for the relays?
Correct : D. All of these
2. Which among these are the main characteristics of a fuse element?
Correct : D. All of the above
3. What is the making capacity of the circuit breaker?
Correct : B. Greater than the asymmetrical breaking capacity of the breaker
4. In a circuit breaker the contact space is ionised by what?
Correct : C. Thermal ionisation of gas.
5. A three phase, 33 kV oil circuit breaker is rated 1200 A, 2000 MVA, 3s. What is
its symmetrical breaking current?
Correct : C. 35 kA
6. What should be the value of fusing factor?
Correct : C. Less than one
7. What is the relation between the fusing current and the diameter of the wire?
Correct : B. I = k d3/2
8. The making and breaking currents of a 3 phase ac circuit breakers in power
systems are respectively in ________form.
Correct : D. instantaneous value, instantaneous value
9. Why is an isolator installed?
Correct : A. To isolate one portion of the circuit from another
10. Assertion (A): In comparison to making capacity of a circuit breaker its breaking
capacity is normally higher. Reason (R): The breaking capacity of a CB is expressed as √3 * VI * 10-6 MVA
Correct : D. A is false but R is true.
11. What is the cut off current in the fuse?
Correct : A. Maximum value actually reache(D)
12. Which circuit breaker is preferred to be installed in extra high voltage AC
system?
Correct : C. SF6 circuit breaker
13. A three phase circuit breaker is rated 2000 MVA, 33 kV. What will be its making
current?
Correct : D. 89 kA
14. A fuse wire of circular cross section has a radius of 0.8mm. The wire blows off at a current of 9(A) What will be the radius of the wire that will blow off at a current of 1A?
Correct : B. 0.18 mm
15. Which among these tests are performed to check the nation or international
standards?
Correct : A. Type test.
16. Refer to the following facts to answer the question A 50 Hz, 11 kV, 3 phase alternator with earthed neutral having a reactance of 3 ohms per phase and is connected to a bus bar through a circuit breaker, if the distributed capacitance upto CB between the phase and neutral is 0.01 μ F. What is the frequency of oscillations?
Correct : C. 12628 Hz
17. What is switchgear?
Correct : D. All of the above.
18. What is / are the main disadvantage / s of using oil as the quenching medium in the circuit breakers?
Correct : D. All of the above.
19. Which of the following circuit breakers has the lowest operating voltage?
Correct : B. Air break
20. The most efficient torque producing actuating structure for the induction type
relays is
Correct : C. Induction cup structure
21. Plug setting of a electromagnetic relay can be altered by varying
Correct : A. Number of ampere turns
22. Which material is used for the manufacture of bus bars?
Correct : B. Copper rods.
23. Which device sends the information to the circuit breaker to interrupt the circuit
in case of fault?
Correct : B. Relay
24. When does the circuit breaker operate in the line?
Correct : C. Whenever the fault occurs in the line.
25. What is the primary principle of a fuse?
Correct : D. Prevent excess current from flowing into the line.
26. On what factor does the operating speed of the relay depend?
Correct : D. All of these
27. Protective relays can be designed to respond to ___________.
Correct : D. All of these
28. What is the purpose of back up protection?
Correct : D. To guard against failure of primary
29. What is the major cause of the failure of the circuit breaker?
Correct : D. All of these
30. Why are the isolators used?
Correct : C. Breaking the circuit under no load condition
31. The isolators used in the transmission lines are capable of breaking
Correct : C. Charging current
32. For which among the following the current ratings are not required?
Correct : C. Isolators
33. What is the making to breaking current ratio for an extra high voltage circuit breaker?
Correct : A. More than 1
34. The breaking capacity of a three phase circuit breaker is given by
Correct : B. √3 * Service line voltage * rated symmetrical current in amperes * 10-6 MVA
35. Which of the following circuit breaker is highly reliable and has a least maintenance?
Correct : D. SF6 circuit breakers
36. The rating of the circuit breaker is usually determined on the basis of ____________ fault.
Correct : A. Symmetrical
37. Which among these circuit breakers produce the least arc energy?
Correct : C. Air blast
38. A thermal protection switch provides protection against what?
Correct : A. Overload
39. What does protective relay provide?
Correct : B. Close the contacts when the actuating quantity attains a certain predetermined value.
40. What is the main purpose of oil in oil circuit breakers?
Correct : B. Quenching ar(C)
41. What is the advantage of using oil as the arc quenching medium?
Correct : D. All of these.
42. When does the arc interruption in oil circuit breaker take place?
Correct : C. Current goes through zero
43. For rural electrification in India, which circuit breaker is generally used?
Correct : C. Vacuum
44. Keeping in view the cost and the overall effectiveness, which of the following circuit breaker is best suited for capacitor bank switching?
Correct : A. Vacuum circuit breaker
45. To limit current chopping in vacuum circuit breakers, the contact material employed should have the properties of
Correct : A. Low conductivity and high vapour pressure.
46. SF6 gas is imported in _____________.
Correct : C. Liquid form in cylinders
47. During arc extinction SF6 gas gets converted to which among these?
Correct : A. Gets decomposed to SF4 and SF2
48. What is the most important property which makes the SF6 very efficient medium for circuit breaking?
Correct : D. Is highly electronegative gas
49. What is the normal pressure at which the SF6 gas is maintained in the closed position of the breaker?
Correct : C. 2.8 kg / cm2
50. What is the major drawback of using SF6 circuit breakers?
Correct : D. Both (a) and (b)
51. Why do the SF6 gases have an excellent heat transfer property?
Correct : D. Both (a) and (c)
52. What is the breaking capacity of the air blast circuit breaker?
Correct : C. 7000 MVA
53. In axial blast type of CB, expansion of air takes place from ______________.
Correct : A. High pressure to low pressure.
54. The air blast circuit breakers for 400 kV systems are designed to operate in how
much time?
Correct : C. 50 ms
55. What is the type of air blast in cross blast type CB?
Correct : B. The blast of air cuts across the ar(C)
56. Why is the resistance switching used in a air blast circuit breaker?
Correct : C. Damp out the fast transient.
57. When using air blast circuit breaker, current chopping is a phenomenon observed
when
Correct : C. A transformer on no load is switched off.
58. Which type of air is used in air blast circuit breaker?
Correct : B. Air free from moisture
59. What is the maximum current upto which fuses can be used?
Correct : D. 100 A
60. What is fusing factor?
Correct : A. The ratio of current rating of the fuse to the minimum fusing current
61. For a current upto 10A which material is used as the fusing element?
Correct : C. Alloy of lead and tin
62. Which among these is the least expensive protection for over current in low
voltage system?
Correct : A. Rewirable fuse.
63. Which among the following statement is true related to fuse?
Correct : A. Greater the current smaller is the time taken by the fuse to blow out.
64. How is the restriking voltage measured?
Correct : B. Peak value
65. What is the interrupting medium in the contactor?
Correct : D. All of the above.
66. Recovery voltage is the value of rms voltage that reappears across the poles of a
circuit breaker before_______________
Correct : B. Final arc extinction
67. Why is it difficult to interrupt a capacitive circuit?
Correct : B. The restriking voltage can be high.
68. Rate of rise of restriking voltage depend on_____________?
Correct : D. Both (b) and (c)
69. On what factor does the rate of rise of restriking voltage (RRRV) depend?
Correct : D. Both (b) and (c).
70. In a circuit breaker, the active recovery voltage depends upon which among
these?
Correct : C. Both (a) and (b)
71. What is restriking voltage?
Correct : A. The transient voltage that appears across the circuit breaker contacts at the instant of arc extinction.
72. For a high speed circuit breaker what will the total clearing time?
Correct : C. 1 to 2 cycles.
73. The interrupting time of a circuit breaker is the period between the instant of
_________.
Correct : B. Energizing the trip circuit and the arc extension on an opening operation.
74. In a circuit breaker, ionisation is facilitated by_________________.
Correct : D. All of the above.
75. Which of the following should have low value for the contacts and their material?
Correct : B. Contact resistance.
76. The heat produced at the contact point owing to flow of electric current is least
affected by_____________________.
Correct : A. Temperature of the surrounding medium.
77. The resistance of an electric arc can be increased by
Correct : C. Splitting the ar(C)
78. By using low resistance method for arc extension what is the value of arc
resistance?
Correct : C. Arc resistance is low
79. What happens in the arc extinction using high resistance method?
Correct : B. Arc resistance is increased with time.
80. What is the arc voltage in a circuit breaker?
Correct : A. In phase with the arc current.
81. Arcing voltage will be the least in case of
Correct : C. Silver
82. How is the initiation of electric arc at the instant of contact separation caused?
Correct : C. Both (a) and (b)
83. The arc resistance depends on which among the following factors?
Correct : D. All of the above.
84. Which type of tripping is generally preferred for the circuit breaker?
Correct : B. Automatically
85. Which part of the circuit breaker is helpful in breaking the current?
Correct : B. Contacts.
86. When a fault occurs in a high voltage transmission line, what happens first?
Correct : B. Relay operates and then the circuit breaker.
87. Upto what voltage can the liquid type HRC fuses be used?
Correct : B. 132 kV
88. What is the main advantage of using a fuse?
Correct : D. All of above.
89. On what basis is the selection of fuse done?
Correct : C. Both (a) and (b)
90. Upto what voltage a cartridge type of fuse can be used?
Correct : D. 33 kV
91. In a HRC fuse what is the time between the cut off and the final current zero
called?
Correct : B. Arcing time.
92. Which material is used in the liquid type of fuse?
Correct : C. Carbon tetra chloride.
93. What is the advantage of HRC fuses over Rewirable fuses?
Correct : D. All of the above.
94. If the strands of the fusing wire are twisted, what happens to the fusing current?
Correct : B. Reduces.
95. What is the typical value of the pre arcing time?
Correct : C. 0.001
96. Outdoor switchgear is generally used for voltage beyond
Correct : C. 66 KV
97. The least expensive protection for over current in low-voltage system is
Correct : A. Rewirable fuse
98. Purpose of backup protection is
Correct : D. To guard against failure of primary
99. We do not require any protection against prime mover failure in case of
Correct : A. Turbo generator sets
100. For the protection of stator winding of an alternate against internal fault involving
ground the relay used is a